Merge Two Sorted Linked Lists Java Program - The Coding Shala

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Merge Two Sorted Linked Lists Java Program

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

Example:

Input: 1->2->4, 1->3->4

Output: 1->1->2->3->4->4

Merger two Sorted Linked Lists Java Program

Approach 1:

Using iterative. We can make a new Linked list.

Java Code 

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if(l1 == null && l2 == null) return null;
        if(l1 == null) return l2;
        if(l2 == null) return l1;
        ListNode dummy = new ListNode(0);
        ListNode head = dummy;
        while(l1 != null && l2 != null){
            if(l1.val <= l2.val){
                dummy.next = l1;
                l1 = l1.next;
            }else{
                dummy.next = l2;
                l2 = l2.next;
            }
            dummy = dummy.next;
        }
        if(l1 != null) dummy.next = l1;
        if(l2 != null) dummy.next = l2;
        return head.next;
    }
}

Approach 2:

Recursive method.

Java Code 

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if(l1 == null) return l2;
        if(l2 == null) return l1;
        if(l1.val < l2.val){
            l1.next = mergeTwoLists(l1.next, l2);
            return l1;
        }else{
            l2.next = mergeTwoLists(l1, l2.next);
            return l2;
        }
    }
}

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